Sanidin k ar dating
Biotites and potassium feldspar have 0% Ar intercept ages around 20-30 Ma, indicative of early Miocene cooling during extension and unroofing in the Colorado River Extensional Corridor.
The approximate intercept age of the hornblende in Granite Wash Mountains is likewise ~80 Ma, indicating that this grain saw a pulse of reheating at that time. The argon loss profiles within the other phases suggest a Miocene overprint on previously-cooled samples. Knapp and Heizler (1990) provide further evidence for rejuvenated Miocene unroofing from the complexities of K-feldspar closure temperatures.
Ar dating is a major method that researchers have used to understand the structural evolution of the Maria Fold and Thrust Belt.
We interpret this dispersion to reflect cooling of the magma reservoir margins below ∼475 °C, accumulation of radiogenic Ar, and rapid preeruption remobilization.
Accordingly, these data elucidate the recycling of subsolidus material into voluminous rhyolite magma reservoirs and the effect of preeruptive magmatic processes on the Ar system.
(a) A constant concentration profile indicates no diffusion or later heating events. (b) Recent diffusive loss of Ar yields a staircase-type profile.
(c) A reheating event yields another staircase-like profile; the 0% value is the age of the reheating event, and the 100% value is the minimum age of initial crystallization of the sample. Knapp and Heizler (1990) use argon-argon thermochronometry to date the thermal history of the Maria Fold and Thrust Belt.
Recent improvements in analytical and microsampling techniques for multiple geochronometers have resulted in datasets with unprecedented temporal and spatial resolution.